Among conventional water-resistant structures of electronic apparatuses, etc., a structure is known in which a cross-sectional area of a rectangular frame-shaped groove holding an O-ring press fitted therein is made smaller on the corners than the cross-sectional area of the rectangular frame-shaped groove on other parts, i.e., sides, in adjustment to the deformation of the O-ring that results when the O-ring is press fitted (see, e.g., Japanese Laid-Open Patent Publication No. 2001-91996). Another water-resistant structure is also known in which the width of a groove holding a liquid packing material injected therein is made larger on corners than the width of the groove on the sides to increase the packing material holding capacity (see, e.g., Japanese Laid-Open Patent Publication No. H7-39043).
However, according to the conventional water-resistant structure using the O-ring, the O-ring becomes hard at the corners where the cross-sectional area of the groove is smaller than the cross-sectional area on the sides and therefore, the O-ring loses elasticity. This leads to a problem that water-resistance becomes inferior at the corners of the O-ring.